Methane fermentation process can be restricted and even destroyed by the accumulation of propionate because it is the most difficult to be anaerobically oxidized among the volatile fatty acids produced by acetogenesis. To enhance anaerobic wastewater treatment process for methane production and COD removal, a syntrophic propionate-oxidizing microflora B83 was obtained from an anaerobic activated sludge by enrichment with propionate. The inoculation of microflora B83, with a 1:9 ratio of bacteria number to that of the activated sludge, could enhance the methane production from glucose by 2.5 times. With the same inoculation dosage of the microflora B83, COD removal in organic wastewater treatment process was improved from 75.6% to 86.6%, while the specific methane production by COD removal was increased by 2.7 times. Hydrogen-producing acetogenesis appeared to be a rate-limiting step in methane fermentation, and the enhancement of hydrogen-producing acetogens in the anaerobic wastewater treatment process had improved not only the hydrogen-producing acetogenesis but also the acidogenesis and methanogenesis.
A laboratory scale up-flow anaerobic sludge bed (UASB) bioreactor fed with synthetic wastewater was operated with simultaneous methanogenesis and denitrification (SMD) granules for 235 days with a gradient decrease of C/N. Molecular cloning, qRT-PCR and T-RFLP were applied to study the methanogenic community structures in SMD granules and their changes in response to changing influent C/N. The results indicate that when C/N was 20:1, the methane production rate was fastest, and Methanosaetaceae and Methanobacteriaceae were the primary methanogens within the Archaea. The richness and evenness of methanogenic bacteria was best with the highest T-RFLP diversity index of 1.627 in the six granular sludge samples. When C/N was reduced from 20:1 to 5:1, the methanogenic activity of SMD granules decreased gradually, and the relative quantities of methanogens decreased from 36.5% to 10.9%. The abundance of Methanosaetaceae in Archaea increased from 64.5% to 84.2%, while that of Methanobacteriaceae decreased from 18.6% to 11.8%, and the richness and evenness of methanogens decreased along with the T-RFLP diversity index to 1.155, suggesting that the community structure reflected the succession to an unstable condition represented by high nitrate concentrations.
Methane production from low-strength wastewater (LSWW) is generally difficult because of the low metabolism rate of methanogens. Here, an up-flow biofilm reactor equipped with conductive granular graphite (GG) as fillers was developed to enhance direct interspecies electron transfer (DIET) between syntrophic electroactive bacteria and methanogens to stimulate methanogenesis process. Compared to quartz sand fillers, using conductive fillers significantly enhanced methane production and accelerated the start-up stage of biofilm reactor. At HRT of 6 h, the average methane production rate and methane yield of reactor with GG were 0.106 m3/(m3·d) and 74.5 L/kg COD, which increased by 34.3 times and 22.4 times respectively compared with the reactor with common quartz sand fillers. The microbial community analysis revealed that methanogens structure was significantly altered and the archaea that are involved in DIET (such as Methanobacterium) were enriched in GG filler. The beneficial effects of conductive fillers on methane production implied a practical strategy for efficient methane recovery from LSWW.
Trimethylolpropane (TMP) wastewater is one of the most toxic petrochemical wastewater. Toxicants with high concentrations in TMP wastewater often inhibit the activity of microorganisms associated with biological treatment processes. The hydrolysis acidification process (HAP) is widely used to pretreat petrochemical wastewater. However, the effects of HAP on the reduction of wastewater toxicity and the relevant underlying mechanisms have rarely been reported. In this study, an HAP reactor was operated for 240 days, fed with actual TMP wastewater diluted by tap water in varying ratios. The toxicity of TMP wastewater was assessed with the inhibition ratio of oxygen uptake rate. When the organic loading rates were lower than 7.5 kg COD/m3/d, the toxicity of TMP wastewater was completely eliminated. When the actual TMP wastewater was directly fed into the reactor, the toxicity of TMP wastewater decreased from 100% to 34.9%. According to the results of gas chromatographymass spectrometry analysis, four main toxicants contained in TMP wastewater, namely, formaldehyde, 2-ethylacrolein, TMP and 2-ethylhexanol, were all significantly removed, with removal efficiencies of 93.42%, 95.42%, 72.85% and 98.94%, respectively. Compared with the removal efficiency of CODCr, the reduction rate of toxicity is markedly higher by HAP. In addition, the change of microbial community in the HAP reactor, along the operation period, was studied. The results revealed that, compared with the seed sludge, Firmicutes became the dominant phylum (abundance increased from 0.51% to 57.08%), followed by Proteobacteria and Bacteroidetes (abundance increased from 59.75% to 25.99% and from 4.70% to 8.39%, respectively).
Conventional biological removal of nitrogen and phosphorus is usually limited due to the lack of biodegradable carbon source, therefore, new methods are needed. In this study, a new alternative consisting of enhanced biological phosphorus removal (EBPR) followed by partial nitritationanammox (PN/A), is proposed to enhance nutrients removal from municipal wastewater. Research was carried out in a laboratory-scale system of combined two sequencing batch reactors (SBRs). In SBR1, phosphorus removal was achieved under an alternating anaerobic-aerobic condition and ammonium concentration stayed the same since nitrifiers were washed out from the reactor under short sludge retention time of 2–3 d. The remaining ammonium was further treated in SBR2 where PN/A was established by inoculation. A maximum of nitrogen removal rate of 0.12 kg N?m–3?d–1 was finally achieved. During the stable period, effluent concentrations of total phosphorus and total nitrogen were 0.25 and 10.8 mg?L–1, respectively. This study suggests EBPR-PN/A process is feasible to enhance nutrients removal from municipal wastewater of low influent carbon source.
Investigation of demulsification of polybutadiene latex (PBL) wastewater by polyaluminum chloride (PAC) indicated that there was an appropriate dosage range for latex removal. The demulsification mechanism of PAC was adsorption-charge neutralization and its appropriate dosage range was controlled by zeta potential. When the zeta potential of the mixture was between -15 and 15 mV after adding PAC, the demulsification effect was good. Decreasing the latex concentration in chemical oxygen demand (COD) from 8.0 g/L to 0.2 g/L made the appropriate PAC dosage range narrower and caused the maximum latex removal efficiency to decrease from 95% to 37%. Therefore, more accurate PAC dosage control is required. Moreover, adding 50 mg/L sulfate broadened the appropriate PAC dosage range, resulting in an increase in maximum latex removal efficiency from 37% to 91% for wastewater of 0.2 g COD/L. The addition of sulfate will favor more flexible PAC dosage control in demulsification of PBL wastewater.
Inflow and infiltration (I/I) are serious problems in hybrid sewerage systems. Limited sewerage information impedes the estimation accuracy of I/I for each catchment. A new method dealing with I/I of a large-scale hybrid sewerage system with limited infrastructure facility data is proposed in this study. The catchment of representative pump stations was adopted to demonstrate the homological catchments that have similar wastewater fluctuation characteristics. Homological catchments were clustered using the self-organizing map (SOM) analysis based on long-term daily flow records of 50 pumping stations. An assessment index was applied to describe the I/I and overflow risk in the catchment based on the hourly wastewater quality and quantity data of representative pump stations. The potential operational strategy of homological catchments was determined by the assessment index of representative pump stations. The simulation results of the potential operational strategy indicated that the optimized operation strategy could reduce surcharge events and significantly improve the quality of wastewater treatment plant effluent.
The diffusion of municipal wastewater treatment technology is vital for urban environment in developing countries. China has built more than 3000 municipal wastewater treatment plants in the past three decades, which is a good chance to understand how technologies diffused in reality.We used a data-driven approach to explore the relationship between the diffusion of wastewater treatment technologies and collaborations between organizations. A database of 3136 municipal wastewater treatment plants and 4634 collaborating organizations was built and transformed into networks for analysis. We have found that: 1) the diffusion networks are assortative, and the patterns of diffusion vary across technologies; while the collaboration networks are fragmented, and have an assortativity around zero since the 2000s. 2) Important projects in technology diffusion usually involve central organizations in collaboration networks, but organizations become more central in collaboration by doing circumstantial projects in diffusion. 3) The importance of projects in diffusion can be predicted with a Random Forest model at a good accuracy and precision level. Our findings provide a quantitative understanding of the technology diffusion processes, which could be used for waterrelevant policy-making and business decisions.
Nitrous oxide (N2O), a potent greenhouse gas, is emitted during nitrogen removal in wastewater treatment, significantly contributing to greenhouse effect. Nitrogen removal generally involves nitrification and denitrification catalyzed by specific enzymes. N2O production and consumption vary considerably in response to specific enzyme-catalyzed nitrogen imbalances, but the mechanisms are not yet completely understood. Studying the regulation of related enzymes’ activity is essential to minimize N2O emissions during wastewater treatment. This paper aims to review the poorly understood related enzymes that most commonly involved in producing and consuming N2O in terms of their nature, structure and catalytic mechanisms. The pathways of N2O emission during wastewater treatment are briefly introduced. The key environmental factors influencing N2O emission through regulatory enzymes are summarized and the enzyme-based mechanisms are revealed. Several enzymebased techniques for mitigating N2O emissions directly or indirectly are proposed. Finally, areas for further research on N2O release during wastewater treatment are discussed.
Bioelectrochemical systems (BES) have been extensively studied for resource recovery from wastewater. By taking advantage of interactions between microorganisms and electrodes, BES can accomplish wastewater treatment while simultaneously recovering various resources including nutrients, energy and water (“NEW”). Despite much progress in laboratory studies, BES have not been advanced to practical applications. This paper aims to provide some subjective opinions and a concise discussion of several key challenges in BES-based resource recovery and help identify the potential application niches that may guide further technological development. In addition to further increasing recovery efficiency, it is also important to have more focus on the applications of the recovered resources such as how to use the harvested electricity and gaseous energy and how to separate the recovered nutrients in an energy-efficient way. A change in mindset for energy performance of BES is necessary to understand overall energy production and consumption. Scaling up BES can go through laboratory scale, transitional scale, and then pilot scale. Using functions as driving forces for BES research and development will better guide the investment of efforts.
In this research, supercritical carbon dioxide extraction (SFE) showed better extraction effect when compared with Solid- liquid extraction (SLE), Soxhlet extraction (SE) and Ultrasonic extraction (UE), not only in the rate but also the time. The comparison among these three extraction modifiers, including acetone, ethanol and methanol demonstrated that ethanol was preferred to SFE due to its high extraction effect and low toxicology. In addition, parameter of SFE, influence of temperature and pressure were investigated, and the best extraction effect was achieved at the optima conditions, temperature of 40°C and the pressure of 35 MPa. Thus, SFE is a highly effective method for flavonols extraction, requiring minimum energy and producing non-toxic byproduct. SFE-GC system is applied for the evaluation on flavonols that plays a key role in plant resistance to heavy metal, with its content and synthetase gene expression significantly increasing in plant when threatened by heavy metal. Besides, results indicated that flavonols can improve plant resistance to oxidative stress by quenching the redundant ROS in matrix.
For biological nitrogen (N) removal from wastewater, a sufficient organic carbon source is requested for denitrification. However, the organic carbon/nitrogen ratio in municipal wastewater is becoming lower in recent years, which increases the demand for the addition of external organic carbon, e.g. methanol, in wastewater treatment. The volatile fatty acids (VFAs) produced by acidogenic fermentation of sewage sludge can be an attractive alternative for methanol. Chemically enhanced primary sedimentation (CEPS) is an effective process that applies chemical coagulants to enhance the removal of organic pollutants and phosphorus from wastewater by sedimentation. In terms of the chemical and biological characteristics, the CEPS sludge is considerably different from the conventional primary and secondary sludge. In the present study, FeCl3 and PACl (polyaluminum chloride) were used as the coagulants for CEPS treatment of raw sewage. The derived CEPS sludge (Fe-sludge and Al-sludge) was then processed with mesophilic acidogenic fermentation to hydrolyse the solid organics and produce VFAs for organic carbon recovery, and the sludge acidogenesis efficiency was compared with that of the conventional primary sludge and secondary sludge. The results showed that the Fe-sludge exhibited the highest hydrolysis and acidogenesis efficiency, while the Al-sludge and secondary sludge had lower hydrolysis efficiency than that of primary sludge. Utilizing the Fe-sludge fermentation liquid as the carbon source for denitrification, more than 99% of nitrate removal was achieved in the main-stream wastewater treatment without any external carbon addition, instead of 35% obtained from the conventional process of primary sedimentation followed by the oxic/anoxic (O/A) treatment.
When microalgae are simultaneously applied for wastewater treatment and lipid production, soluble algal products (SAP) should be paid much attention, as they are important precursors for formation of disinfection byproducts (DBPs), which have potential risks for human health. Chlorella sp. HQ is an oleaginous microalga that can generate SAP during growth, especially in the exponential phase. This study investigated the contribution of SAP from Chlorella sp. HQ to DBP formation after chlorination. The predominant DBP precursors from SAP were identified with the 3D excitation-emission matrix fluorescence. After chlorination, a significant reduction was observed in the fluorescence intensity of five specific fluorescence regions, particularly aromatic proteins and soluble microbial by-product-like regions, accompanied with slight shifting of the peak. The produced DBPs were demonstrated to include trihalomethanes and haloacetic acids. As the algal cultivation time was extended in wastewater, the accumulated SAP strengthened the formation of DBPs. The trend for DBP formation was as follows: chloroform>dichloroacetic acid>trichloroacetic acid.
Three acid-producing strains, AFB-1, AFB-2 and AFB-3, were isolated during this study, and their roles in anaerobic digestion of waste activated sludge (WAS) were evaluated. Data of 16S rRNA method showed that AFB-1 and AFB-2 were Bacillus coagulans, and AFB-3 was Escherichia coli. The removal in terms of volatile solids (VS) and total chemical oxygen demand (TCOD) was maximized at 42.7% and 44.7% by inoculating Bacillus coagulans AFB-1. Besides, the optimal inoculum concentration of Bacillus coagulans AFB-1 was 30% (v/v). Solubilization degree experiments indicated that solubilization ratios (SR) of WAS reached 20.8%±2.2%, 17.7%±1.48%, and 11.1%±1.53%. Volatile fatty acids (VFAs) concentrations and compositions were also explored with a gas chromatograph. The results showed that VFAs improved by 98.5%, 53.0% and 11.6% than those of the control, respectively. Biochemical methane potential (BMP) experiments revealed that biogas production increased by 90.7% and 75.3% when inoculating with Bacillus coagulans AFB-1 and AFB-2. These results confirmed that the isolated acid-producing bacteria, especially Bacillus coagulans, was a good candidate for anaerobic digestion of WAS.
The effects of food to microorganism (F/M) ratio and alcohol ethoxylate (AE) dosage on the methane production potential were investigated in treatment of low-strength wastewater by a submerged anaerobic membrane bioreactor (SAnMBR). The fate of AE and its acute and/or chronic impact on the anaerobic microbes were also analyzed. The results indicated that AE had an inhibitory effect to methane production potential (lag-time depends on the AE dosage) and the negative effect attenuated subsequently and methane production could recover at F/M ratio of 0.088–0.357. VFA measurement proved that AE was degraded into small molecular organic acids and then converted into methane at lower F/M ratio (F/M<0.158). After long-term acclimation, anaerobic microbe could cope with the stress of AE by producing more EPS (extracellular polymeric substances) and SMP (soluble microbial products) due to its self-protection behavior and then enhance its tolerance ability. However, the methane production potential was considerably decreased when AE was present in wastewater at a higher F/M ratio of 1.054. Higher AE amount and F/M ratio may destroy the cell structure of microbe, which lead to the decrease of methane production activity of sludge and methane production potential.
This work presents an overall introduction to the Station for Observing Regional Processes of the Earth System–SORPES in Nanjing, East China, and gives an overview about main scientific findings in studies of air pollution-weather/climate interactions obtained since 2011. The main results summarized in this paper include overall characteristics of trace gases and aerosols, chemical transformation mechanisms for secondary pollutants like O3, HONO and secondary inorganic aerosols, and the air pollution–weather/climate interactions and feedbacks in mixed air pollution plumes from sources like fossil fuel combustion, biomass burning and dust storms. The future outlook of the development plan on instrumentation, networking and data-sharing for the SORPES station is also discussed.
Polycyclic aromatic hydrocarbons (PAHs) often occur in oil-contaminated soil, coke wastewater and domestic sludge; however, associated PAH degraders in these environments are not clear. Here we evaluated phenanthrene degradation potential in the mixed samples of above environments, and obtained a methanogenic community with different microbial profile compared to those from sediments. Phenanthrene was efficiently degraded (1.26 mg/L/d) and nonstoichiometric amount of methane was produced simultaneously. 16S rRNA gene sequencing demonstrated that bacterial populations were mainly associated with Comamonadaceae Nocardiaceae and Thermodesulfobiaceae, and that methanogenic archaea groups were dominated by Methanobacterium and Methanothermobacter. Substances such as hexane, hexadecane, benzene and glucose showed the most positive effects on phenanthrene degradation. Substrate utilization tests indicated that this culture could not utilize other PAHs. These analyses could offer us some suggestions on the putative phenanthrene-degrading microbes in such environments, and might help us develop strategies for the removal of PAHs from contaminated soil and sludge.
Identifying source information after river chemical spill occurrences is critical for emergency responses. However, the inverse uncertainty characteristics of this kind of pollution source inversion problem have not yet been clearly elucidated. To fill this gap, stochastic analysis approaches, including a regional sensitivity analysis method, identifiability plot and perturbation methods, were employed to conduct an empirical investigation on generic inverse uncertainty characteristics under a well-accepted uncertainty analysis framework. Case studies based on field tracer experiments and synthetic numerical tracer experiments revealed several new rules. For example, the release load can be most easily inverted, and the source location is responsible for the largest uncertainty among the source parameters. The diffusion and convection processes are more sensitive than the dilution and pollutant attenuation processes to the optimization of objective functions in terms of structural uncertainty. The differences among the different objective functions are smaller for instantaneous release than for continuous release cases. Small monitoring errors affect the inversion results only slightly, which can be ignored in practice. Interestingly, the estimated values of the release location and time negatively deviate from the real values, and the extent is positively correlated with the relative size of the mixing zone to the objective river reach. These new findings improve decision making in emergency responses to sudden water pollution and guide the monitoring network design.
Treating water contaminants via heterogeneously catalyzed reduction reaction is a subject of growing interest due to its good activity and superior selectivity compared to conventional technology, yielding products that are non-toxic or substantially less toxic. This article reviews the application of catalytic reduction as a progressive approach to treat different types of contaminants in water, which covers hydrodehalogenation for wastewater treatment and hydrogenation of nitrate/nitrite for groundwater remediation. For hydrodehalogenation, an overview of the existing treatment technologies is provided with an assessment of the advantages of catalytic reduction over the conventional methodologies. Catalyst design for feasible catalytic reactions is considered with a critical analysis of the pertinent literature. For hydrogenation, hydrogenation of nitrate/nitrite contaminants in water is mainly focused. Several important nitrate reduction catalysts are discussed relating to their preparation method and catalytic performance. In addition, novel approach of catalytic reduction using in situ synthesized H2 evolved from water splitting reaction is illustrated. Finally, the challenges and perspective for the extensive application of catalytic reduction technology in water treatment are discussed. This review provides key information to our community to apply catalytic reduction approach for water treatment.
Pulsed plate bioreactor (PPBR) is a biofilm reactor which has been proven to be very efficient in phenol biodegradation. The present paper reports the studies on the effect of dilution rate on the physical, chemical and morphological characteristics of biofilms formed by the cells of Pseudomonas desmolyticum on granular activated carbon (GAC) in PPBR during biodegradation of phenol. The percentage degradation of phenol decreased from 99% to 73% with an increase in dilution rate from 0.33 h–1 to 0.99 h–1 showing that residence time in the reactor governs the phenol removal efficiency rather than the external mass transfer limitations. Lower dilution rates favor higher production of biomass, extracellular polymeric substances (EPS) as well as the protein, carbohydrate and humic substances content of EPS. Increase in dilution rate leads to decrease in biofilm thickness, biofilm dry density, and attached dry biomass, transforming the biofilm from dense, smooth compact structure to a rough and patchy structure. Thus, the performance of PPBR in terms of dynamic and steady-state biofilm characteristics associated with phenol biodegradation is a strong function of dilution rate. Operation of PPBR at lower dilution rates is recommended for continuous biological treatment of wastewaters for phenol removal.
